The present invention relates to a device for steering a conveyor belt in a belt conveyor.
A common problem when operating belt conveyors is the tendency of-the conveyor belt in operation to move laterally relative to the intended path of travel through the conveyor. Lateral displacement, i.e. displacement of the conveyor belt transversely of its direction of travel, may cause, inter alia, damage to the belt by the belt edges coming into contact with fixed parts on the belt conveyor frame.
In order to solve this problem, many conveyors have been provided with one or more support rollers which support the conveyor belt during its return travel and which are manually angularly adjustable relative to the intended direction of travel of the belt. The angular orientation of these support rollers is adjusted during the running-in of the belt conveyor to ensure that in normal operational conditions the belt will travel through the conveyor in a correctly centred manner. If a tendency towards lateral displacement should arise in operation, due for instance to elongation of the conveyor belt during operation or to dirt and deposits accumulating on the end rollers of the conveyor manual postadjustment of the set angular position of these support rollers is necessary. Supplementary work is required therefor and furthermore in many cases the conveyor must be stopped during the adjustment work. By setting a support roller at an angle it is thus possible to compensate for the tendency of the belt to run out of line by moving laterally relative to its intended direction of travel.
Moreover, devices have been suggested serving to automatically adjust the conveyor for adaptation thereof to such lateral motions of the conveyor belt. Such an automatic self-adjusting or self-aligning device is shown and described in NO-C-178853 and the corresponding PCT Publication WO9514627. However, this prior-art device does not aim at adjusting the position of the belt to maintain it in a centred position relative to the centre line of the conveyor frame but at ensuring that the support rollers are constantly directed perpendicular to the conveyor belt, whether the conveyor belt is centred or not. This aim is achieved by arranging for the belt side edges to travel along edge guide rollers arranged at one end of a double-arm lever, whose other end supports a stand in which the support roller is mounted. This mounting stand, which in its simplest form is a plate, is in turn pivotally connected with the double-arm lever. When the latter pivots in response to the engagement of the guide rollers with the belt edges, the support roller will automatically set itself at right angles to the belt travelling direction. In this prior-art device, return of the belt to the intended centre line of the path of travel of the belt might be achieved as a result of the edge guide rollers trying to push the belt back to a centred position.
It has also been suggested that the belt be centred by letting it travel over a support roller stand containing two belt support rollers which are inclined and each engage a lateral edge portion of the belt in order to cup the belt around the central portion of the belt. This technique of achieving centring, however, does not always give the intended result.
An improvement in relation to these prior-art devices is described in SE-C-507733 and the corresponding WO9819943. This device for steering a conveyor belt is capable of automatically returning a conveyor belt to the intended central position along a path of travel. Thus the steering device causes the conveyor belt to move as much as possible in a centred fashion over support rollers, drive rollers and end rollers in a belt conveyor.
This prior-art device for steering a conveyor belt starts from the idea, known per se, of using a belt roller to compensate for the tendency towards lateral displacement of the belt. What differs this belt steering device from those previously known is that the angular orientation of the support roller occurs automatically and that the degree of obliqueness is determined by the extent of the lateral movement of the conveyor belt relative to the intended path of travel along the belt conveyor. For detecting the degree of displacement of the conveyor belt relative to the intended path, use is made of belt position detecting means which are connected with the belt support roller via a linkage system for pivoting in the principal plane of the belt and setting of the belt support roller in a pivoting position, in which the belt support roller, owing to its engagement with the belt, exerts a readjusting force on the belt, so that the conveyor belt is steered back and is centred relative to the intended path of travel of the belt. According to SE-C 507733 and the corresponding WO9819943, the belt readjusting means thus is a belt support roller which engages the belt and rolls against the same and which is pivotable in the principal plane of the belt, and the belt position detecting means is connected with the belt support roller via a linkage system for pivoting and adjusting the belt support roller in a pivotal position, in which the belt support roller, owing to its engagement with the belt, exerts a readjustment force on the belt.
This prior-art conveyor belt steering device functions very well but suffers from one drawbackxe2x80x94it functions merely in one belt travelling direction. This means that the prior-art conveyor belt steering device cannot be used in conveyor belt installations having a reversible direction of travel of the conveyor belt since, when reversing the direction of travel of the belt, the belt position detecting means and the belt readjusting means must change places and also the linkage system must be turned around.
An object of the invention therefore is to provide a new conveyor belt steering device which functions well independently of the direction of travel of the conveyor belt and which therefore can be used also for conveyor belt installations with reversible conveyor belts.
The invention is based on the per se known idea of using belt position detecting means which detect the lateral position of the conveyor belt relative to the intended path of travel of the belt and which are operatively connected with belt readjusting means which actuate the conveyor belt to be returned to the intended centred position along the intended path of travel of the belt. The novel feature of the invention is how the belt readjusting means is designed and connected with the belt position detecting means and how the readjustment of the conveyor belt occurs.
That characterising the invention is stated in the independent claim while the dependent claims define particularly preferred embodiments of this invention.
To sum up, the invention can be considered to reside in belt position detecting means and belt readjusting means being arranged on a roller cradle which is connected with a frame by means of inclined links for pivoting and setting the belt roller in a pivoting position, in which the belt support roller is inclined to exert, by engaging the belt, a readjustment force on the same.